The outside of the center is where Doctor Sun is found during the day. When the Sole Survivor first approaches the establishment, Doctor Sun will greet them hurriedly no matter if they wish to utilize his services or not. He will point them to the main entrance if they ask for facial reconstruction information.
The exterior stand has containers and a chemistry station. Going through the door outside will lead to a basement where Doc Crocker can be be found (before The Disappearing Act) and performs facial reconstruction for 100 caps. Going into the surgery cellar through a hatch, one will be in a cave/basement with a bloody table and chains hanging from the ceiling.
The cellar will remain unlocked upon finishing the Disappearing Act.
The mega surgery center appears only in Fallout 4.